This invention relates generally to electro-optical devices such as liquid crystal devices.
Liquid crystal displays use a spatial light modulator (SLM) made up of a top plate and a substrate which surround a liquid crystal material. Conventionally, the region for the liquid crystal material is defined by spacer balls which may be distributed over the substrate. In addition, it is known to fabricate insulating spacers directly on a silicon substrate. The function of the spacers is to maintain the distance between the top plate and the substrate and to define the region for the liquid crystal.
Liquid crystal devices using liquid crystal over a silicon substrate (LCOS) technology may form large screen projection displays or smaller displays (using direct viewing rather then projection technology). Typically, the liquid crystal material is suspended over a thin passivation layer. A glass plate with an indium tin oxide (ITO) layer covers the liquid crystal, creating the liquid crystal unit sometimes called a cell. The glass layer is typically suspended over the liquid crystal by a gasket that surrounds the cell array.
A silicon substrate may define a large number of pixels. Each pixel may include semiconductor transistor circuitry in one embodiment. The pixel may have a top reflective layer. An electrical potential may be applied to an electro-optical material using the reflective layer. A transparent top plate may have an inner transparent conductive layer that acts as an electrode that works with the reflective layer. An electrical field generated at each pixel may alter optical characteristics of an electro-optical material between the silicon substrate and the top plate. For example, the polarization of light passing through the electro optical material may be altered. As another example, the electro-optical material may change its light transmission characteristics.
In conventional electro-optic devices, the electro-optic material is aligned in a preferential direction by alignment layers on either side of the electro-optic material. The alignment layers may be made of polyimide or polyvinyl alcohol (PVA). The alignment layers may be formulated by rubbing an indium tin oxide coated glass with a nylon coated velvet cloth. This action may create microgrooves such that electro-optic molecules align along the microgrooves thereby becoming aligned preferentially.
For transmissive liquid crystal modulators the alignment layers are rubbed on the top and bottom indium tin oxide plates. In reflective modulators such as a liquid crystal over silicon modulators, the bottom electrode layer is a metal layer over silicon. Rubbing on this surface may be cumbersome and may require protection measures against electrostatic discharge. Therefore alignment layers are created by oblique deposition of thin layers of silicon oxide.
Controlling the electro-optic properties is a tricky and laborious task which may take several literations to get the manufacturing process right. Further, the alignment process is dependent on the type and nature of the electro-optic material used. Thus, there is continuing need for better ways to create the desired alignment in electro-optic materials such as liquid crystals.